The Question of the Month Answers, September 2007, Microwave Journal, May 7, 2007, published Oct. 17, 2007 (which can be found at http://www.microwavejournal.com/articles/print/4771) describes a protection circuit for an assembly connected to the protection circuit. The protection circuit is designed using stripline or coaxial technology on a support having discrete elements. The support in turn is mounted in a suitable housing which also contains the connections for actuation and the high-frequency signals. The high-frequency output is connected to the input of the assembly to be protected via a high-frequency line.
A disadvantage of this arrangement is that the protection circuit is of discrete design or, if integrated, is implemented using diodes. Both approaches are cost intensive and unsuitable for applications in which there is only little space available. When diodes are used, the additional problem arises that the limiter diodes used do not have adequate properties to ensure a high capacity for the limiter circuit.
A further limiter circuit is known from U.S. Pat. No. 5,301,081. This circuit comprises a first circuit block having a transistor and a second circuit block having a diode arrangement. The transistor in the first circuit block is actuated by means of a complex detector circuit comprising a plurality of diodes. A disadvantage of this limiter circuit is the complicated design and the large number of components required.
Exemplary embodiments of the present invention are directed to a limiter circuit that eliminates the disadvantages of the prior art.
In the case of the limiter circuit according to the invention having a signal input and a signal output for limiting an output signal that is applied to the signal output and that can be supplied to a further circuit connected to the output of the limiter circuit, a connection for supplying a bias voltage and a transistor are present, wherein the gate connection of the transistor is connected to the connection via a first matching circuit and to the signal input via a second matching circuit.
By way of example, the matching circuits comprise resistors and/or inductances and/or capacitances and/or portions of line elements. This allows the operating point of the transistor to be adjusted according to the requirements. By way of example, it is thus possible to adjust the frequency response or the input matching of the transistor as appropriate.